What is the proper way to say this to my students who played a sick joke on a peer?

A student with sever mental health disorders walked into class, and the whole class of 25+ kids were sobbing and wailing. I thought someone had passed away. I asked wtf was going on, and was told that everyone was crying because I had announced that the boy (let's call him Timmy) wasn't allowed to come to school for some unknown reason.<br><br>I was absolutely flabbergasted, because this had NOT been announced to me. Further, Timmy walked into class..so he most certainly wasn't banned.<br><br>I asked my superiors about it, and no one knew anything about this. So I asked Timmy. Timmy told me that his "girlfriend" (we're only 7th grade) had texted him saying that I had announced that he was forbidden from coming to class. Then, his classmates (who were also in on the joke) were texting him, "yeah I'm so upset that you can't come anymore I'm going to miss you so much." That sort of thing. Timmy was not happy about it, and was very hurt.<br><br>I have to tell my students that this was not acceptable, but how do I put it into words? This was an absolutely horrible thing to do, but how do I tell them why? Further, how do I get them to realize that it was a horrible thing to do, and make it stick? I don't want any other students to be put in this situation, because this is one of the worst things I've heard of kids doing to one another. <br><br>I want to make it very clear that I am not defending the kids, and that I absolutely think this was a horrible thing to do, and I am going to tell them that as well. I just need help figuring out how to put it all together.